You’re a UA Platinum, and it didn’t smell even the least bit fishy to you that UA would operate a PHL-DCA flight?

This is disclosed extremely poorly on the app; it’s much better on the web. I agree that it’s confusing. The right thing to do probably would have been for agents, either at PHL or at IAD, to put your friend on an IAD-CLE flight. The only tricky part is that UA presumably doesn’t want people to be able to book this kind of itinerary — in order to get saver awards vs everyday awards — and then get agents to “fix” it for them.

Still — what about the receipt? You had 24 hours to review the reservation and fix it at that point. At no point between booking and the airport did anyone ever pull up the itinerary online?

Personally, I’d consider it a lesson learned and move on. Full disclosure: I’ve actually done the same thing for the same reason (Tokyo, not DC, but it’s the same root cause). However, I noticed it immediately and went back and changed it. That probably makes me biased.